The retinal pigment epithelium (RPE) is a single layer of epithelial cells localized between choroid and neuroretina in the eye. It has many important physiological functions including phagocytosis of shed photoreceptor outer segments, transport of nutrients to retina and regeneration of the visual pigment. Several diseases affecting the retina such as macular degeneration are associated with defects in RPE function. We have investigated gene expression in human retinal pigment epithelial cells. ARPE-19, a cell line derived from human retinal pigment epithelium (Dunn et. al., Exp. Eye Res., 62: 155, 1996), was employed. A cDNA library was constructed using poly A+ RNA fractions isolated from ARPE-19 cells. In order to characterize the library, several individual clones were analyzed by DNA sequencing. A cDNA clone, thus obtained, appeared to represent a hitherto unknown gene. Northern blot analysis indicated that this gene is highly expressed in ARPE-19 cells, the size of the mRNA being ~5 kb. A high level expression of this gene was also detected in testis and placenta when RNA fractions from various tissues were hybridized with a cDNA probe. The complete cDNA sequence was elucidated with 5 and 3 RACE techniques. The cDNA sequence was found to encode a protein consisting of 980 amino acids. The predicted sequence had the characteristics of a soluble protein and contained distinct nuclear localization signals. The protein also contained 6 ankyrin repeats indicating that it could interact with other proteins. A genomic clone was isolated by PCR screening. This gene was found to be localized to human chromosome 5. We have characterized a novel gene that is highly expressed in human retinal pigment epithelial cells. The physiological role of this gene remains to be elucidated. - Retinal pigment epithelium, RPE, ARPE-19 cells, ankyrin, gene expression